pki: set keys permission to world readable and owned by root

This enables all applications to access the keys.

Each key is protected by its own permissions, so we are not exposing
anything new. Engine does not generate new keys so no need to be
writable by engine.

Change-Id: Iedd916d41aca4f80a25c9ab13a240b57a5577b0b
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>